Several publications and patent documents are cited throughout the specification in order to describe the state of the art to which this invention pertains. Each of these references are incorporated herein as though set forth in full.
Directed differentiation of pluripotent stem cells into a variety of cell types opens new possibilities for regenerative medicine (1-6). Epithelial stem cells (EpSCs) in the hair follicle bulge are required for hair follicle growth and cycling, while also contributing to wound healing (7-10). Human EpSCs (hEpSCs) in the hair follicle express CD200, ITGA6 and cytokeratin-15 (KRT15)(11, 12) but their isolation and propagation for tissue engineering purposes remains a challenge. Generating sufficient numbers of hEpSCs is crucial for treatment of hair loss and other degenerative skin diseases (9, 13).
It has been shown that human embryonic stem cells and iPSCs can be differentiated into keratinocytes. However, these keratinocytes exhibit an epidermal squamous cell phenotype and thus do not have the capacity to regenerate hair follicles. To date, no successful protocols have been developed to make human hair follicles. Human hair follicle epithelial stem cells have been characterized and they express markers such as K15 or CD200. However, these cells can not be cultured or expanded in vitro because these stem cells rapidly lose stem cell marker expression and function in vitro.